1. Field of the Invention
The present invention relates to an improvement in the control device for use in an image forming apparatus such as a copier or a printer, and more particularly to an improved information transmission system between plural computers for use in such image forming apparatus to be controlled by said plural computers.
2. Description of the Prior Art
In the control of a copier with two computers, there is already known a system for avoiding the inconvenience in the one-computer control by using one of the computer mainly for sequence control such as the control of the copying process while using the other for real-time control such as receiving of copying key signal or control of segment display.
In such control system, the copying process is initiated by the transmission of a copy execution instruction from the computer for real-time control to the computer for sequence control. At the same time, however, there may be required additional data, particularly mode data such as the size selection signals for the copying sheets set in the copier. Such signals, if supplied to both computers, will require a larger number of input ports as the number of sizes increases. On the other hand, even if such signals are supplied only to one computer, the deficiency in the input ports may still arise since the information has to be transmitted to the other computer. Particularly it is impossible to reduce the number of input/output ports in the commercially available microcomputers as they have a determined number of ports.
Also in the conventional control system with plural computers, the sequence control computer Q2 releases a signal in each copying cycle, in response to which the other control computer Q1, for example, for key entry, drives a copy counter in said control computer. Also upon detection of a copy disabled state such as sheet jamming, the sequence control computer Q2 supplies a signal to the control computer Q1 which thus prohibits the entry of the copy start signal. Furthermore a signal transmission is required when the jammed state is resolved. The transmission of such signals requires a large number of input/output ports.
Furthermore, there are required many input/output ports in order to correct the above-mentioned copy counter in the control computer Q1, when the sheets are lost, for example, in the sheet jamming, according to the number and location of such jammed sheets.
Furthermore additional ports are needed in order to handle complicated signal transmission in case plural copy start modes are present for both computers, such as the manual insertion copy mode in which the copy cycle is started by the manual insertion of a copy sheet in addition to the ordinary copy mode in which automatic sheet feeding from a cassette is initiated by the copy start key.
Furthermore, in the conventional control system with plural computers, a malfunction in a computer resulting, for example, from a fluctuation in the power supply voltage or an erroneous operation, may cause the copier to stop in an undesirable state or to run uncontrollably, or to ignore the instructions entered by the operator. Although there is already proposed a system in which the computer resets itself upon detection of an abnormality therein, it is difficult to synchronize the timing of resetting in case plural computers are involved.
In the conventional image forming apparatus, the scanning of an original document is achieved by illuminating said original with a suitable light source such as a fluorescent lamp and guiding the reflected light into a photosensitive member composed, for example, of cadmium sulfide, or a solid-state imager such as a charge-coupled device. In such scanning there is generally employed a slit exposure method achieving either by displacing a carriage supporting the original or by displacing an optical system comprising mirrors or the like for guiding said reflected light to the photosensitive member or to the solid-state imager.
In order to obtain a high-speed image forming apparatus, the original carriage or the optical system has to be displaced at a correspondingly high speed. For example in an apparatus performing 30 cycles of scanning per minute, the original carriage or the optical system has to perform a reciprocating motion in every two seconds.
The original carriage or the optical system of such speed is stopped at a desired position by deactivating a drive source for a moving member in response to the position thereof detected by detecting means. However, although the detection signal for stopping the moving member is generated in this manner, the moving member can only be stopped with a certain delay due to the inertia thereof or a delay in response of the driving means. Consequently such stopping method gives rise to an uncontrollable error in the stopping position of the moving member, so that the succeeding scanning cycle has to be started from a fluctuating position. For this reason, in the conventional apparatus, the moving member is forced to stop mechanically in order to attain a constant stop position. However such stopping method may generate undesirable vibration or eventually cause damage to the apparatus, particularly in case of a higher moving speed as mentioned above.